The present invention relates to gear drives, and particularly to a diaphragm mounted detuner for preventing clatter or vibration of an idling pinion engaged with a driven gear.
In a variety of gear drives, of which marine drives are one example, there are two sets of gears that are used to transmit power from the motor or engine to the driven element, such as the propeller shaft. In a marine drive there is an ahead gear train that will drive the ship in a forward direction and a reverse gear train that will drive the ship backwards. Each of the gear trains typically includes a pinion mating with a common bull gear that in turn drives the ship's propeller. The ahead pinion and the reverse pinion are selectively engaged with the engine by a system of clutches.
The majority of time a marine drive is connected for the forward mode of operation with the ahead pinion driving the bull gear. During this time the reverse pinion continues to be in mesh with the bull gear but it is not transmitting power and is simply idling. Since the means of propulsion is usually a diesel engine and the driven member is a propeller, there are torsional impulses present in the drive train. As a result, the elements of the drive are not moved with a constant rotational velocity. When the reverse pinion is idling in mesh with the bull gear, it is subjected to the torsional impulses which it picks up from the bull gear and this often causes the reverse pinion to clatter because of the tooth clearance (backlash) in the meshing teeth of the reverse pinion and bull gear. Noises and tooth loads can be produced which are objectionable.
One approach to detuning the resulting vibrations is illustrated in U.S. Pat. No. 3,682,015 issued Aug. 8, 1972 to William S. Richardson. That approach involves forming a helical tooth pinion with a major tooth portion which can transmit the load to the bull gear under power and a minor tooth portion mounted at one end of the major tooth portion by a torsionally resilient means such as a coil spring or a rubber key. The teeth of the minor tooth portion are thicker than the teeth of the major tooth portion so that when the pinion is idling the teeth of the minor tooth portion will contact the teeth of the bull gear and hold the teeth of the major tooth portion out of engagement with the bull gear. The torsionally resilient means are selected to have sufficient stiffness so that the major tooth portion will not contact the teeth of the bull gear unless the pinion is powered to drive the bull gear. The vibrations are taken up within the torsionally resilient elements.
A second approach is illustrated and described in my copending application Ser. No. 199,087 filed Oct. 20, 1980 for "Gear Drive Detuner." This approach also employs a helical tooth pinion having a major tooth portion and a minor tooth portion but the thickness of the teeth is the same. The minor tooth portion is formed on a detuner pinion which is slidably mounted adjacent the end of the reverse pinion and is biased towards the reverse pinion so that the teeth of the detuner pinion and of the reverse pinion will be wedged in the tooth spaces of the helical bull gear when the pinion is idling. In addition to overcoming vibrations, this approach also accommodates variations in the physical size of the driving components such as bull gear run-out, dimensional changes due to thermal growth, and variation in size due to wear. One drawback to this approach is that friction must be overcome in order to allow the detuner pinion to move axially to accommodate the dimensional changes while continuing to tend to wedge its teeth and the teeth of the reverse pinion in the tooth spaces of the driven gear.
In the present invention I have developed an assembly which mounts the detuner pinion in such a way as to substantially reduce the frictional forces which it will encounter in accommodating itself to dimensional variations.